1. Field of the Invention
The invention herein relates to an exercise device and more particularly to a treadmill commonly used for physical exercise and training.
2. Overview of Prior Art
The treadmill for use as a physical exercise device has evolved from the use of conveyors in industry. These systems are used to transport items from one place to another and are typically comprised of an endless belt that travels over front and rear pulleys, one of which is mechanically connected to a drive system such as an electric motor. Since the belt must be pliable to bend around the pulleys the space between the pulleys must be supported because the pliable belt would likely not be able to support the weight of the objects being transported thereon. As a solution what is commonly used is a plurality of rollers with their axes oriented parallel to the end pulleys. The rollers are free to support the weight of the object adding only a minimal amount of friction to the system.
Exercise treadmills necessitate supporting loads in excess of 21/2 to 3 times the users body weight (Cavanagh and Lafortune) and (Nilsson and Thorstensson). The maximum foot contact with the running surface during running is around 54% (Kaliszer, et al) and given an estimate of 35 sq. in. of surface area of a runner's foot the resultant pressure is over 31 psi (214 KPa) for a 200 pound runner on a flat surface. If a runner is forced to run on a set of rollers this pressure could increase by 5 times or more. Though this load produces a pressure that is slightly less than 1% of the yield stress of bone (121 MPa) (Skalak and Chien), the stretch receptors in the skin detect discomfort. This pressure used in a in vivo model for compression response of skin (Dikstein and Hartzshtark) results in a deformation of 133 meters. Clearly far beyond the 2-4% seen in the linear region of stress-strain response of skin. The resultant helps to explain why we see potential for long term injury due to even seemingly small changes in running mechanics. Changes in how the runner's foot strikes or leaves the surface may cause problems (Chadbourne). Trying to run on a set of rollers could greatly alter running gait due to the body's response to the increased foot pressure.
The industry has adapted a minimally functional model for people to run on that has remained virtually unchanged for several decades. Traditional samples are seen in U.S. Pat. No. 5,542,892 to Buhler where a belt (14) is supported by a pad (46) which is supported by a flat and substantially rigid deck (48). The belt is an endless belt which is kept in tension by a front and rear drum pulley. A motor drives a pulley and the friction between the underside of the belt and the surface of the pulley allows the belt to move across the surface of the deck, which is the running surface. The pad assists in absorbing the impact of the user's foot on the running surface.
The obvious problem is the friction between the belt and the deck or pad. As previously calculated, a great deal of pressure is generated between these surfaces. Not only does this predispose the belt to wear but the system must maintain enough kinetic energy to pull the user's foot over the deck without it slowing. This would generate a "cogging" effect and greatly disrupt the user's running gait. The Buhler patent disclosure includes a antifriction or wax block (49) to try to reduce the coefficient of friction between these surfaces. The dichotomy is that the system requires a good deal of friction between the belt and the pulley but necessitates minimal friction between the belt and the deck.
A similar disclosure is made by Skowronski et al in U.S. Pat. No. 5,599,259. Here a rear front belt pulley (22) and a rear belt pulley (28) are chambered to assist in the tracking of the belt (20). The belt is supported by the deck (50) with additional structures to give the deck flex to help absorb the impact of running. The drive transmission (111) and motor (104) is shown to drive the rear pulley (28) in the large unit and the front pulley in the small unit.
This is one of the few disclosures that identify the advantage of rear pulley drive as it is associated with this type of device. Since the belt is pliable it can only transmit load effectively in tension not in compression, thus fewer fibers are stressed due to the tension requirement to pull the runner's foot caused by the friction between the belt and the deck when the rear pulley drives the belt rather than the front pulley. This is because the rear pulley is closer to the application of the load and therefore the frictional force. Smaller units cannot fit the motor between the upper and lower runs of the belt so the motor is placed in the front and the front pulley drives the belt.
Methods to overcome this friction problem have been addressed by several individuals. One such attempt is made by Schonenberger in U.S. Pat. No. 4,334,676 and also in U.S. Pat. No. 4,614,337. Here a movable surface treadmill is disclosed where the surface is comprised of a plurality of step or slat elements that are attached to an endless belt, the belt being driven by one of the front or rear pulleys. The slat elements are supported on the upper run by a series of support rollers that are supported by the frame of the unit. This creates an upper run that includes only rolling friction of the slats on the support rollers and not sliding friction between a belt and a deck.
The conception and application works well except other than the complexity of the device. The resultant is comprised of much of the existing components of a traditional treadmill while adding a combination of slats that are connected to the belt and an array of support rollers on each side of the slat members. The combination is a device that is not price competitive in the market place.
A specialty device is disclosed by Lepine et al., in U.S. Pat. No. 5,385,520, in the form of an ice skating treadmill. This device is similar to the previously disclosed in that it is comprised of a front and rear pulley which supports an endless belt, only the belt is covered with ridged plastic slats. The reinforced belt is supported on each side of the upper run by a set of roller supports. The combination does eliminate the sliding friction associated with a traditional treadmill, as does the previous disclosure but here as before the physical size is prohibitive to many applications, even if it was modified to be used for an individual on which to run. In addition, the traditional problems associated with belt tracking on the drum pulleys, the weight and cost of such a device would make it prohibitive.
A horse exerciser is disclosed by Pike in U.S. Pat. No. 4,361,115. This has parallels to the previously disclosed in that individual slats are secured to links of two parallel roller chains instead of a continuous belt. The front and rear drum pulleys are replaced by two pair of sprockets which guide and/or drive the combination. The upper run of the plurality of slats are supported by an arrangement of roller supports positioned along the sides of the upper run, as previously done. Tracking of the segmented belt is now extremely critical. If one side of the one bearing support which supports the sprocket combination drifts a slight amount the associated sprocket will not align with the chain links and jump the track. This not only would result in ceasing the operation of the device while in use, which could result in injury to the user, but as the motor continues to attempt to drive the unit, damage to the device would likely result. Since roller chain commonly stretches with normal use due to the wear on the pivoting components, and no idler function is employed the likelihood is great.
If the device was scaled down for human use this problem would be even more likely because as the sprocket size is decreased the size of the roller chain, the tooth depth also decreases, thus increasing the risk of disengagement. Also the labor intensive cost associated with securing a slat to each roller chain link would make such a device very expensive and not practical in the marketplace.
Another animal treadmill is disclosed by Rhodes in U.S. Pat. No. 5,277,150 which is specified for use by dogs. The treadmill portion of the device is similar to the previously disclosed in that it is comprised of a pair of end rollers disposed at either end of the supportive surface. parallel planks are fastened to a pair of belt member called runners. The runners articulate with a plurality of support roller bearings in the span between the end rollers. There is no apparent disclosure of a resistance or power means to drive or slow the movement of the treadway relative to the dog. This lack of resistance or power would make this device virtually non-functional for human use.
An alternative to the roller chain of the earlier referenced is disclosed by Schonenberger in U.S. Pat. No. 5,470,293. As with all belt or chain track devices which are driven by one of two drum pulleys (or sprockets), the inability of the track and the pulley to slip is important for this is what drives the running surface. Here the inventor discloses drum or deflection pulleys which includes a sliding disk member and a toothed-disk member. The sliding disk member includes a V-belt area to assist in the transmission of force to drive the belt. The use of the V-belt reduces the noise as compared to the toothed belt, thus the combination allows a smaller toothed belt and even an intermittent toothed disk. The tracking advantages of the toothed arrangement and the quiet of the V-belt still speak to the inherent problems of drum pulleys to drive a belt, even if the belt is has a laminate of structure elements to eliminate the need for a treadmill deck.
Another moving supportive surface is disclosed by Lee et al in U.S. Pat. No. 4,938,473 in that of a treadmill with a trampoline surface. Here an endless trampoline surface is supported on the sides by roller brackets which run on support rail on each side of the endless belt including curved portions on the front and rear of the device. Springs connect the brackets to the endless belt, the combination generating a spring like running surface. Another version is disclosed in which a pair of end rollers is used to support the endless belt on the front and rear of the treadmill. In this case a drive means is mentioned in the text as being powered to rotate the belt, but specifics are not described beyond that. In the version which includes a curved rail portion on the ends shows a hidden end pulley in FIG. 4, but no apparent reference beyond that. In this case, no drive means is disclosed nor anticipated by this disclosure due to the absence of the end pulleys which drive the belt.
A cushioned surface such as this is prone to excessive deflection of the running surface resulting in an unstable running surface. This predisposes the runner to potential excessive inversion and eversion of the subtalar joints in the feet of the runner. Since the center of rotation of the subtalar joint is above (superior) to the bottom of the foot, where contact is made with the running surface, and loading comes from above, through the ankle this joint, this places the joint in unstable equilibrium, thus predisposing this and other joints of the lower body to excessive rotation and potential damage. This is supported by the findings of Chadbourne which cites the occurrence of acute injuries from running on soft surfaces.
The Lee et al patent does disclose a method of reducing the vertical displacement of the foot on the running surface by the placement of a "deck" under the belt. The upper surface of the deck is disclosed in FIG. 10 to be comprised of "an upper frictionless surface 72, a middle cushioning surface of foam, for example, 73, and a lower structural surface of metal, wood or the like, designated by the numeral 74". This is unreasonable because first of all a "frictionless" upper surface does not exist. The resultant combination would functionally be no different than that of Buhler or Skowronski et al which were previously disclosed and the limitations cited are apparent here as well here.